The present invention relates to the detection of a perforation in the wall of a liquid storage container. More particularly, the present invention relates to an improvement to the method described in U.S. Pat. No. 4,462,249, commonly assigned to the assignee of the present invention and hereby incorporated in its entirety by this specific reference thereto, for detecting such perforations by evacuating the tank and acoustically detecting the bubbles that are formed in the liquid stored in the container as a result of the passage of air through any perforation(s) that may be present.
Although the method described in U.S. Pat. No. 4,462,249 is used successfully and extensively for the testing of such liquid storage containers as the underground gasoline tanks of a service station, there are instances in which it is useful to either confirm the result of that testing method or to increase the leak detection capability. The latter is particularly desirable in that, although at present, the applicable federal regulations prohibit leakage of gasoline from such facilities at a rate exceeding 0.1 gallons per hour, on information and belief, those regulations are soon to be changed to perhaps reduce that maximum permissible rate by half. Further, the ability to detect smaller leaks may yield useful data as to the expected life of a particular storage tank that can be used to plan the maintenance of the tank and to prevent the occurrence of an environmentally significant leak.
Such tanks also present some unique leak detection problems for which increased detection capability is useful. For instance, many such tanks do not themselves have perforations that cause the loss of gasoline therefrom; the leak is actually located in the connections and/or lines leading out of the tank. The leak may also be in the vapor recovery line. Likewise, if the tank is installed below the water table or the perforation is near the bottom of the tank and the tank is nearly filled with gasoline, the leak may be difficult to detect by the method described in U.S. Pat. No. 4,462,249.
It is therefore an object of the present invention to provide a method of confirming the presence of a leak in a liquid storage tank or other container.
Another object of the present invention is to provide a method having increased leak detection capability.
Another object of the present invention is to provide a method of detecting a leak in a liquid storage container regardless of the location of the perforation from which the liquid leaks in the tank and regardless of whether the perforation is located above or below the level of the liquid in the container.
Another object of the present invention is to provide a method having increased leak detection capabilities for use in a liquid storage container that is only partially filled with liquid.